1. Field of the Invention
This invention relates generally to a clutch that produces a drive connection between components when their relative rotation is in one direction, and overruns when relative rotation is in the opposite direction. In particular, the invention pertains to such a one-way or overrunning clutch having rockers, which engage and disengage in response to selectable actuation.
2. Description of the Prior Art
Conventional one-way clutches for producing a one-way drive connection between inner and outer races of the clutch include sprags or rollers for driveably connecting the races and the components of a mechanical assembly connected to the races. Such clutches are commonly used in the powertrain or driveline of an automotive vehicle. One-way clutches perform satisfactorily in many cases, but certain applications, such as those in which large magnitudes of torque are transmitted by the clutch, or those that provide only a small space for the clutch, require one-way clutches other than conventional sprag-type or roller-type clutch to meet desire requirements.
Conventional one-way clutch assemblies have at least one sprag or roller, which driveably locks two notched or pocketed races together mutually in one rotary direction and allows the races to rotate freely in the other direction. Rocker and sprag type one-way clutch assemblies can increase the torque capacity for a given package size compared to those of a roller-type clutch, but they are generally limited in torque transmitting capacity by the magnitude of the contact or bearing stresses caused by contact of the rockers or sprags with the races.
To overcome these and other difficulties, a one-way overrunning clutch described in U.S. Pat. No. 5,070,978 includes a drive member and a driven member, which are mounted for clockwise and counterclockwise rotation about a common axis. The drive member includes a planar drive face, normal to the common axis, which connects with a source of power for rotating the planar drive face either clockwise or counterclockwise. The driven member includes a planar driven face, positioned in close proximity to and in confronting relationship with the drive face. The drive and driven members are coupled to one another through a series of pockets in one of the drive faces, and a plurality of cooperating struts carried by the other face, such that when the drive member is driven counterclockwise, it drives the driven member with it. When the drive member is driven clockwise, it does not drive the driven member, but rotates freely relative to the driven member. Column stability of the strut, which transmits the torsion load between the races, is an importance factor in the design.
U.S. Pat. No. 5,954,174 discloses a ratchet one-way clutch assembly having an inner race with notches, an outer race with pockets, and rockers located in the pockets to engage the notches. The rockers have a pivot ridge which mates with a peak or recess in the pockets in the outer race to position the rocker in the pocket. The center of mass of each rocker is located such that the rocker tends to engage or disengage a notch in the inner race. A spring is used to provide a tilting force on each rocker directed to produce engagement of the rocker with a notch.
Conventional one-way clutches develop relatively large magnitudes of hoop stress in the races when torque is transmitted through the clutch; therefore, the races of conventional one-way clutches are formed of bearing grade steel in order to withstand the operating hoop stress. Because the clutches disclosed in the '978 and '174 patents develop relative low operating hoop stresses in service, those clutch can be formed of sintered powder metal. Clutches formed from powder metal potentially can be produced at relative low cost compared to the cost to form and produce a conventional clutch of high grade steel, provided extensive machining is avoided.
The clutches described in the '978 or '245 patents, however, require a significant amount of machining of the components that are formed of powder metal. Excessive internal backlash, which can produce noise at unacceptable levels, is a potentially problem under certain operating conditions with these clutches.
In an automatic transmission for a motor vehicle, hydraulically-actuated friction clutches and brakes engage and disengage to produce a range of speed ratios, which accelerate the vehicle from rest with relative high torque and low vehicle speed and thereafter maintain the vehicle at highway speed, a lower torque condition. Often the transmission contains a low-reverse brake, which alternately holds a planet carrier against rotation during operation in the first forward gear and reverse gear, and release the carrier to rotate in all other gears. A one-way clutch could produce the function of a hydraulically-actuated low-reverse brake at lower cost and with less complexity, such as by producing non-synchronous gear changes between first gear and second gear and between first gear and reverse gear, but a one-way should be selectably actuated to perform these functions.
A need exists, therefore, for a low cost, reliable one-way clutch that is be formed readily from powder metal and can be controlled to produce the range of operations required in response to selectable, coordinated actuation with other transmission functions. The clutch should occupy little space, minimize in-service noise, and require little or no machining. Preferably, the desired clutch should include features that facilitate its assembly in a drive system.